1. Field of the Invention (Technical Field)
The present invention relates generally to apparatuses for cooling exhaust gases, particularly exhausts from internal combustion engines, and specifically relates to a multi-pass recirculation cooler.
2. Background Art
It is known in the general art of internal combustion engines to provide some system of turbocharging, whereby a turbine harnesses energy from exhaust gases to power a compressor. The compressor is then used to increase engine performance, typically by boosting the pressure of air supplied to the engine.
Nearly as important as engine performance is the need for cleaner exhausts. Most internal combustion engines in the United States are subject to regulations from the U.S. Environmental Protection Agency governing pollutant levels in engine emissions. “Stationary sources” such as internal combustion engine powered generators and the like, as well as motor vehicles, are required to maintain emissions of certain pollutants, such as CO and NOx, below legal limits. Pollution control, however, ideally is accomplished while compromising engine performance as little as possible.
One mode of reducing the emissions of internal combustion engines—regardless of whether the engine is turbocharged, but frequently when it is—is through exhaust gas recirculation (EGR). EGR involves the return to the engine's intake manifold of some portion of the engine exhaust. Exhaust gases are diverted from the exhaust manifold through a duct or conduit for delivery to the intake manifold, thereby allowing exhaust to be introduced to the combustion cycle, so that oxygen content is reduced, which in turn reduces the high combustion temperature that contributes to excessive NOx formation.
The EGR method of reducing exhaust emissions has drawbacks. A specific problem is that EGR is most effective when the gases are cooled, which problem can be solved in part by using heat exchangers. It is known to provide “multi-pass” coolers in conjunction with EGR systems, whereby the heated exhaust passes two or more times through the heat exchanger core. Exhaust gas enters an EGR cooler at very high temperature and exits at much lower temperature, resulting in a large change in gas density as it transits the cooler. Consequently, the exhaust gas has a high velocity in the first pass, but much lower velocities in the second and any subsequent passes through the core. The high gas velocity causes high parasitic pressure losses in the first pass, and the reduced velocity in the subsequent passes results in low heat transfer. Gas side fouling of the system is inversely related to gas velocity, so the low gas velocity in the second and subsequent passes through the core increases the potential for deleterious fouling.
Against the foregoing background, the present invention was developed. The scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.